示例1(var ints = new List { 1, 2, 3};):使用Eumerable.ToList会导致31.5%的额外开销,而List.Add()会导致8.7%的开销。
而示例2:在List.ctor上引起11.8%的开销,在Ensure Capacity上引起5%的开销。
(来自Red Gate ANTS性能分析工具的结果)
您可以看到,使用var ints = new List { 1, 2, 3};需要通过反汇编执行更多操作。
var intsx = new[] {1, 2, 3}.ToList()
0000003f mov edx,3
00000044 mov ecx,60854186h
00000049 call FFF5FD70
0000004e mov dword ptr [ebp-4Ch],eax
00000051 lea ecx,[ebp-50h]
00000054 mov edx,872618h
00000059 call 61490806
0000005e lea eax,[ebp-50h]
00000061 push dword ptr [eax]
00000063 mov ecx,dword ptr [ebp-4Ch]
00000066 call 614908E3
0000006b mov ecx,dword ptr [ebp-4Ch]
0000006e call dword ptr ds:[008726D8h]
00000074 mov dword ptr [ebp-54h],eax
00000077 mov eax,dword ptr [ebp-54h]
0000007a mov dword ptr [ebp-40h],eax
var ints = new List<int> { 1, 2, 3 }
0000007d mov ecx,60B59894h
00000082 call FFF5FBE0
00000087 mov dword ptr [ebp-58h],eax
0000008a mov ecx,dword ptr [ebp-58h]
0000008d call 60805DB0
00000092 mov eax,dword ptr [ebp-58h]
00000095 mov dword ptr [ebp-48h],eax
00000098 mov ecx,dword ptr [ebp-48h]
0000009b mov edx,1
000000a0 cmp dword ptr [ecx],ecx
000000a2 call 608070C0
000000a7 nop
000000a8 mov ecx,dword ptr [ebp-48h]
000000ab mov edx,2
000000b0 cmp dword ptr [ecx],ecx
000000b2 call 608070C0
000000b7 nop
000000b8 mov ecx,dword ptr [ebp-48h]
000000bb mov edx,3
000000c0 cmp dword ptr [ecx],ecx
000000c2 call 608070C0
000000c7 nop
000000c8 mov eax,dword ptr [ebp-48h]
000000cb mov dword ptr [ebp-44h],eax
}